Fukushima Update- Part 1
First of all let’s survey the damage. Reactors 1, 2, and 3 suffered core meltdowns that breached the steel containment vessels leaving leaks that have been releasing highly radioactive cooling water AND molten nuclear fuel into the concrete basement below the vessel.
This is kind of a containment vessel too and while there are no current indications that nuclear reactions are continuing in the escaped fuel slag that would burn through this floor and into the uncontained earth foundation of the plants, they’re not waterproof and there is no doubt at all that millions of gallons of highly radioactive water and perhaps some fine particulates are leaking into the environment uncontrolled.
This has led to a re-evaluation of cooling and clean-up strategies that continues because there are no really good answers. Several radiation peaks indicating continued nuclear reactions in the melted and puddled fuel mean you can’t stop pumping water and the leaking makes it difficult to maintain a sufficient amount in the containment vessel to moderate the reaction (that’s why you get the peaks when the level dips too low).
There’s a continued risk of hydrogen explosions too and one of the reasons I mention that is because the one bit of good news is that it does not look as if the large spent fuel pond at the non working (at the time of the accident) Reactor 4 is having uncontrolled reactions.
At the moment.
A lot of the damage was caused by hydrogen explosions which in turn was caused by malfunctioning vents of the same type currently in use at many U.S. Nuclear Power Plants.
(note: There is something wacky going on with my quote from Scarecrow that I am attempting to correct)
The Times report to which Scarecrow refers is this one-
In Japan Reactor Failings, Danger Signs for the U.S.
By HIROKO TABUCHI, KEITH BRADSHER and MATTHEW L. WALD, The New York Times
Published: May 17, 2011
TOKYO – Emergency vents that American officials have said would prevent devastating hydrogen explosions at nuclear plants in the United States were put to the test in Japan – and failed to work, according to experts and officials with the company that operates the crippled Fukushima Daiichi plant.
The failure of the vents calls into question the safety of similar nuclear power plants in the United States and Japan. After the venting failed at the Fukushima plant, the hydrogen gas fueled explosions that spewed radioactive materials into the atmosphere, reaching levels about 10 percent of estimated emissions at Chernobyl, according to Japan’s nuclear regulatory agency.
…
Tokyo Electric in recent days has acknowledged that damage at the plant was worse than previously thought, with fuel rods most likely melting completely at Reactors 1, 2 and 3 in the early hours of the crisis, raising the danger of more catastrophic releases of radioactive materials. The company also said new evidence seemed to confirm that at Reactor No. 1, the pressure vessel, the last layer of protection, was broken and leaking radioactive water.The improved venting system at the Fukushima plant was first mandated for use in the United States in the late 1980s as part of a “safety enhancement program” for boiling-water reactors that used the Mark I containment system, which had been designed by General Electric in the 1960s. Between 1998 and 2001, Tokyo Electric followed suit at Fukushima Daiichi, where five of six reactors use the Mark I design.
Most the damage at Reactor 4 was cased by an explosion in the vents that it SHARED with Reactor 3.
But there is also this follow up report, also from the Times–
NRC Finds Many U.S. Nuclear Plants Ill-Prepared to Handle Simultaneous Threats
By PETER BEHR of ClimateWire, The New York Times
Published: May 19, 2011
Something under one-third of the 104 U.S. reactors were found to have some vulnerabilities to extreme emergencies, according to the NRC, which is preparing a summary of its post-Fukushima findings.
…
At a time when the NRC and industry leaders are calling for a rigorous safety culture within the U.S. nuclear industry, the inspection findings raise questions about whether some plants were following the letter of requirements but not prepared for “unthinkable” events.
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The plant owners’ responses to beyond design basis threats are usually voluntary. “We keep saying, ‘Oh, these are beyond basis events therefore we don’t’ get involved.’ We are happy that the industry responded. We look at it once. That’s it. In the future it’s up to them. I am really bothered by that.”
This piece contains details safety issues at a number of U.S. Nuclear Plants including Indian Point (NYC) and Millstone (Connecticut).
Coming next- The Big TEPCO Bailout.
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